A variety of methods of measuring a sample thickness by using a transmission electron microscope have been proposed heretofore. A method widely used in recent years is a method of calculating a thickness from a mean free path of inelastic scattering using a distribution of electron energy loss (refer, for example, to R. F. Egerton, Electron energy-loss spectroscopy in the electron microscope (1996, Plenum Press, New York) pp. 301 to 312). Although this method is very simple, it is known that a value of a mean free path is inaccurate, and in addition the value changes with sample contamination, a natural oxide film or the like and it is possible to measure only a relative thickness.
A most general method of measuring an absolute film thickness is a method of measuring a film thickness by acquiring a convergent beam electron diffraction image in a two-wave excited state and using an appeared interference fringe (refer, for example, to J. C. H. Spence and J. M. Zuo, Electron Microdiffraction (1992, Plenum Press, New York) pp. 86 to 88). Some problems have been pointed out for this method, however; it is necessary to slant a sample greatly in order to make the sample enter a two-wave excited state and to know in advance an extinction distance.
A method of measuring a crystal bending distortion by using a transmission electron microscope has also been proposed.
A method of measuring a sample thickness and a crystal bending distortion at high precision has been proposed in recent years by comparing a convergent beam electron diffraction image obtained through experiments with an image obtained through calculation (refer to T. Yamazaki, A. Kashiwagi, K. Kuramochi, M. Ohtsuka, I. Hashimoto, and K. Watanabe, Journal of Electron Microscopy 57 (2008) pp. 181 to 187). This method has a relatively high precision and measurements are possible if calculation software is available. In using this method, if calculation is performed each time a calculation image coincident with the experiment image is searched, it is very inefficient. It is therefore desired to configure a database of calculation images. It is, however, necessary to prepare a huge database capacity in order to compare a whole two-dimensional image between a calculation image and an experiment image. An image rotation operation is also necessary for image matching.